An internal combustion engine in which a fuel injection valve for direct injection for injecting fuel into a combustion chamber and a fuel injection valve for port injection for injecting fuel into an intake port are provided has already been disclosed in Japanese Patent Application Publication 2000-18137. In Japanese Patent Application Publication 2000-18137, in a predetermined operation condition, the port injection fuel injection valve is operated, and fuel supply to the engine is shared by the direct injection fuel injection valve and the port injection fuel injection valve.
As mentioned above, in a case where the direct injection fuel injection valve and the port injection fuel injection valve are used in combination, as compared with a configuration in which one of the fuel injection valves covers the total fuel injection amount, it becomes possible to reduce the sizes of the fuel injection valves themselves, and the minimum fuel injection amounts of the fuel injection valves become small, and consequently, in particular, setting accuracy of the fuel injection amount in a region in which the fuel injection amount is small is improved. On the other hand, if the fuel injection amounts of the injection vales are individually controlled, the control becomes complicated, and it also becomes difficult to maintain the setting accuracy of the total fuel injection amount. In addition, as to the direct injection, as compared with the port injection, it is superior in responsiveness and controllability, and fuel injection timing is close to ignition timing, and stratified charge combustion can be realized. Functionally, it is therefore preferable that the direct injection covers the total fuel injection amount. However, if an operation condition in which the port injection fuel injection valve is not operated is prolonged, operation failure tends to occur such as clogging of the port injection fuel injection valve.